Roadside noise barrier helps to reduce downwind pollutants concentration
from vehicle emission. This positive characteristic of the construction feature
can be explained by its interaction with flow distribution and species
transportation. In this thesis, 3-D numerical model has been developed to
simulate highway pollutant transportation - realizable k-e model was employed
to model turbulent flow; non-reaction species dispersion was applied to
simulate species transport. First, numerical models were validated with
experimental data. Good agreement was observed. Then detailed simulations were
conducted to study double barriers’ effects on highway pollutant dispersion
under different settings: noise barriers with different heights, noise barriers
with and without edge effects, different atmospheric thermal boundary
conditions. Results show that: (1) Noise barrier feature helps reduce downwind
pollutant concentration. For 4m tall double barriers without edge effect case,
80% less concentration can be found than non-barrier case at downwind 100m; (2)
Reduction of concentration increases as barrier height increases. 1m higher can
lead 0.002
more concentration reduction at ground level. (3) Unstable
condition has the least concentration and stable condition has the highest
concentration at the same location. (4) Barrier with edge effect has higher
concentration than barrier without edge effect downwind; (5) Oblique wind
condition enlarges barrier edge effect. The larger the oblique angle is, the
higher turbulence intensity can be found near barrier edges. These findings
will be provide valuable input to noise barriers design so as to improve
roadside neighborhood air quality.